Method for reducing mercury vapor contamination of the ambient atmosphere from liquid mercury

ABSTRACT

A process for reducing mercury vapor contamination from residual spilled liquid mercury to the ambient atmosphere. The principal step is covering the surface on which the spill occurred with a coating that is essentially impervious to mercury vapor. Also, preliminary steps of spreading a metal powder onto the spilled mercury which will amalgamate with the mercury, using a weak acid catalyst if necessary, and/or scrubbing the floor prior to the application of the coating may be employed. Further, a wearresistant coating may be applied over the mercury vapor coating and/or the ambient atmosphere may be filtered after the application of the mercury barrier film.

United States Patent Karpinski METHOD FOR REDUCING MERCURY VAPOR CONTAMINATION OF THE AMBIENT ATMOSPHERE FROM LIQUID MERCURY Inventor: Medard F. Karpinski, Parma, Ohio Assignees: Kenneth F. Karpinski; Clarence M.

Karpinski, both of Parma, Ohio Filed: Mar. 8, 1973 Appl. No.: 339,207

US. Cl. 134/4; 134/10; 209/48;

427/343; 427/401; 427/407 Int. Cl. B0813 7/00 Field of Search 209/50, 48, 51, 15;

References Cited UNITED STATES PATENTS 9/1973 Fornofi' et a1 55/74 June 10, 1975 Primary Examiner-William D. Martin Assistant ExaminerDennis C. Konopacki [57] ABSTRACT A process for reducing mercury vapor contamination from residual spilled liquid mercury to the ambient atmosphere. The principal step is covering the surface on which the spill occurred with a coating that is essentially impervious to mercury vapor. Also, preliminary steps of spreading a metal powder onto the spilled mercury which will amalgamate with the mercury, using a weak acid catalyst if necessary, and/or scrubbing the floor prior to the application of the coating may be employed. Further, a wear-resistant coating may be applied over the mercury vapor coating and/or the ambient atmosphere may be filtered after the application of the mercury barrier film.

16 Claims, No Drawings METHOD FOR REDUCING MERCURY VAPOR CONTAMINATION OF THE AMBIENT ATMOSPHERE FROM LIQUID MERCURY BACKGROUND OF THE INVENTION This invention relates generally to reduction of mercury vapor contamination to the ambient atmosphere, and is especially adaptable for use in dental offices to protect from contamination of the office from mercury vapor produced by liquid mercury spilled on floors and on various other surfaces.

It has recently been determined that spilled liquid mercury can produce a substantial health hazard by contaminating the surrounding ambient atmosphere with mercury vapor which volitilizes from the spilled liquid mercury. This problem is especially prevalent and especially critical in dental offices which have a past history of having mercury spilled therein. Dentists very frequently work with mercury to make amalgams for teeth filling and occasionally such mercury has been spilled on table tops and floors. Since the problem of mercury vapor contamination has not long been recognized, the task of cleaning up the spilled mercury was never considered as critical or crucial; and therefore, it was a normal practice of dentists and other technicians working with mercury to merely try to remove all the mercury visible on the floor without worrying about the small amounts that would get down into the cracks and crevices and hence, not amenable to being removed by ordinary cleaning means. However, it has recently been recognized that these comparatively small amounts of liquid mercury which can accumulate in cracks and crevices and other surface irregularities in a dentists office can provide a mercury vapor level in the office high above the safe limits for such mercury contamination. Naturally the longer the period of time over which these mercury spills have occurred the more the liquid mercury will accumulate, and hence the higher level of contamination. In fact, it has been found that in many dental offices which have been used for a great period of time, the mercury vapor contamination is extremely unsafe.

Because of the nature of the metallic mercury, especially in view of its very high surface tension, and propensity to break into exceedingly fine droplets, it is literally impossible to remove all of this mercury from its location in various cracks on the surfaces on which it has been spilled in dental offices. Even thorough scrubbing by ordinary means will not eliminate the mercury and, in fact, in most cases will not even reduce the amount of mercury sufficiently to bring the mercury vapor contamination below the safe level. Indeed, the question of mercury contamination is an extremely serious question since the effects of mercury on the human body are cumulative and thus prolonged exposure to even minute amounts of mercury vapor or other mercury contamination can result in accumulating sufficient amounts to bridge the toxic level. Thus, it is desirable to reduce the mercury vapor contamination in any area to absolute minimum, especially where people are in continuous proximity to this area day in and day out.

SUMMARY OF THE PRESENT INVENTION According to the present invention, a method of reducing mercury vapor contamination from droplets of mercury exposed on a surface is provided. The essential step of this method is coating the surface with a liquid composition which will solidify to a continuous film which film is substantially impervious to mercury vapor. Also, preferably, the surface is scrubbed with water prior to the application of the coating and this wash water vacuum-removed from the surface, the vacuumed fluid passing through a water filter unit to entrap in the water filter any mercury. Also, in some cases it is desirable prior to the scrubbing with water to apply a metal powder to the surface, the powder being of a metal which will amalgamate with the mercury. Also, in many cases it is desirable to filter the ambient atmosphere through a mercury vapor entrapping filter such as activated charcoal, subsequent to the coating of the surface. In order to increase the wear characteristics, it is also sometimes desirable to apply an acrylic polymer coating on top of the mercury vapor barrier coatmg.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is specifically directed toward reducing to a minimum the mercury vapor contamination in the ambient atmosphere surrounding any surface on which droplets of mercury are dispersed. As indicated above, this is principally directed toward dental offices and more particularly to the floors of dental offices. Hence, the invention will be described as particularly applicable to the floors of dental offices, although it is to be understood that it is not so limited and may be used on any surface wherein it is desired to reduce the mercury vapor contamination from droplets of mercury on a surface. The heart and essential step of the invention is the coating of the surface with a liquid composition which will solidify to a continuous film which is substantially impervious to mercury vapor, i.e., a mercury vapor barrier film. It is to be understood that there will be a certain small amount of mercury vapor penetration of any film. Thus, as used herein, if a film will maintain mercury vapor concentration below the government accepted maximum in the ambient atmosphere which is 0.1 Mg/M it can be considered substantially or essentially impervious. Of course, the lower this value, the better barrier the film is. This film should be a non-toxic, and should have good wear properties and should not be removable by ordinary cleaning means and cleaning solutions such as soap and water, and particularly ammoniated cleaners which are in use now.

It has been found that very good results can be obtained by using polyacrylamides and polyvinyl alcohols, as well as alcohol soluble nylon such as that sold under the trademark ELVANIDE" by E. Du Pont De Nemours & Co. of Wilmington, Del., the preference being for polyvinyl alcohols because of their strong, tough film forming characteristics. Specifically, polyvinyl alcohols, such as those sold under the trade name EL- VANOL, by the E. l. DuPont De Nemours & Company, produce excellent results.

Polyvinyl alcohols come in different grades, the basic differences being the differences in molecular weight and viscosity, which in turn affects the solubility of the film. For example, ELVANOL grades 72-60, 71-30, and -05, which are all hot water soluble grades with excellent resistance to cold water all perform quite well. Also, cold water soluble grade 51-05 works well. The polyvinyl alcohol is mixed with water, to obtain the desired viscosity for spreading and then applied to the surface. The proportions of the mixture should be such as to allow for satisfactory spreadability by whatever means are employed, yet provide on drying a sufficiently thick and dense film. While this may vary some, in the case of ELVANOL 51-05 grade a solution of about by weight of the polyvinyl alcohol has proved satisfactory, spreading by hand with a cloth. This applied liquid coating will then dry on the surface to produce a continuous film, which is non-toxic and non-inflammable wear-resistant, and which is essentially impervious to mercury vapor which will thereby provide a barrier film against volitilizing mercury. For example, on one floor wherein the mercury residue was causing mercury vapor contamination to the surrounding atmosphere measured as being in excess of 0.1 Mg/M, after being coated with a 10% solution of EL- VANOL grade 51-05 as described above, reduced the measured mercury vapor contamination in the surrounding atmosphere to between 0.01 and 0.02 Mg/M.

While certain preferred grades of polyvinyl alcohols, i.e., ELVANOL 72-60, 71-30, and 70-05 are insoluble in cold water, nevertheless if cold water soluble grades are used such as 51-05, or if it is desirable to insure insolubility in hot water as well as cold water, an insolubilizer may be added to the original composition. These insolubilizers or insolubilizing agents include water-soluble amine-formaldehyde condensates such as dimethylolurea, trimethylolmelamine, dimethylolethylene urea and triazone resins; dialdehydes; and polyvalent metal salts or complexes, all as is wellknown in the art. For example, commercial formeldehyde resins such as those sold under the trademark ZESET by Du Pont work quite well.

When this composition has dried, a very good, tough, wear-resistant film is formed which will be amenable to repeated washings and which will resist wearing off and provide an acceptable floor finish. However, if it is desired to even more enhance the wear-resistant properties of the finish, a coating of commercial type floor finishes can be applied, preferably the acrylic polymer type which are sold under many different trade names. This will not increase materially the resistance to the mercury vapor, but it will provide some amount of increase to wear-resistance, and, in fact, will provide a second layer or buffer film above the mercury barrier film which can be replaced as it wears off and can be easily removed and replaced while maintaining the mercury vapor barrier film intact.

in order to insure continued low levels of mercury contamination in the ambient atmosphere around the protected surface, which will protect in case of damage to the barrier film allowing contamination from the underlying sealed in mercury droplets, and also to protect against any future spills which are not sealed in, it is desirable to continuously filter the surrounding atmosphere through a filter which will remove mercury vapot. The best filter material is activated charcoal and it has been found that treated activated charcoal air filter units sold by Barnaby Cheney Company are particularly effective.

In most cases, it is desirable to remove as much of the spilled mercury from the surface as possible prior to application of the mercury vapor barrier film forming composition. This is preferably done by thoroughly scrubbing the surface with water and then vacuuming the scrubbed surface with a vacuum cleaner to remove the scrubbing residue which will contain suspended therein particles of mercury. This vacuumed fluid is then passed through a water filter unit to remove the trapped particles of mercury so that they are not discharged to the ambient atmosphere. One particular type of vacuum cleaner that is especially useful for this purpose is the Rainbow Vacuum Cleaner, manufactured by Rex Air Corporation. (It should be noted that the mercury may be recovered from the water filtering unit and reprocessed and reused.)

in the case of very heavy spills such as a dropped vial of mercury or a dropped thermometer, it is desirable to add an additional preliminary step before the step of scrubbing the surface. This preliminary step comprises applying a granulated or powder metal or metallic compound (hereinafter referred to generically as metal) to the floor, the metal being one which will amalgamate with the mercury. The most desirable of such metals is tin; however, bronze, copper, and zinc have all been utilized satisfactorily and these are merely representative of metals being used. The metal will amalgamate with the mercury to form at least a partial amalgam which serves several beneficial purposes. First, in the amalgamated form mercury does not produce a significant amount of mercury vapor. Also, the amalgamated granules are much more easily removed than liquid droplets of mercury. Thus, this initial preliminary step is desirable where there is a very large substantial amount of mercury to be dealt with. It has also been found that in order to start the amalgamation process, it is desirable to use a catalyst which preferably is in the form of a spray of weak acid. Acetic acid and phosphoric acid have been found to be especially effective for this purpose, applied after the metal powder.

It is desirable to use a substantial excess of the metal powder; i.e., substantially more powder than is necessary to provide a complete amalgamation with the spilled mercury. This is to insure effective amalgamation with as much mercury as possible; also, after the partially amalgamated powder is removed by the vacuum removal step, it can be recovered from the water trap and continued to be utilized. in fact, it has been found that once the amalgamation process has started and this powder is reused it is not necessary to utilize a catalyst to have this process continue on subsequent applications of this partially amalgamated powder.

Extensive tests in dental laboratories, even those wherein spills have occurred over a thirty to forty year period and more, have shown that by utilizing the method of this invention, mercury vapor contamination can be reduced to such an extent that it is well below the safety limits, and in fact, can be reduced to an almost negligible amount. It is to be understood that the principle step involved is the application of the mercury vapor barrier film. The other steps are utilized in combination with this step where necessary as the surrounding circumstances dictate. The essence of the invention, however, is the mercury vapor coating applied over the surface which contains the mercury droplets.

What is claimed is:

l. A method of reducing mercury vapor contamination of the ambient atmosphere from liquid mercury droplets disposed on an exposed surface, which method comprises the step of applying a metal powder to the surface, the metal being one that will amalgamate with mercury, thereafter scrubbing the surface with water and removing the water from the surface with vacuum means, and passing the vacuumed fluid through a water filter unit to entrap in the filter any amalgamated mercury contained in the fluid, and thereafter coating said surface with a liquid composition which will solidify to a continuous film which is substantially impervious to mercury vapor.

2. The invention as defined in claim 1, wherein the metal is selected from a group consisting of tin, bronze, copper, and zinc.

3. The invention as defined in claim 1, further characterized by applying a catalyst to the surface after applying the metal powder.

4. The invention as defined in claim 3, wherein said catalyst is a weak acid.

5. The invention as defined in claim 4, wherein the acid is selected from a group consisting of acetic acid and phosphoric acid.

6. The invention as defined in claim 1, further characterized by filtering the ambient atmosphere through a mercury vapor entrapping filter subsequent to applying said coating.

7. The invention as defined in claim 6, wherein said filter is activated charcoal.

8. The invention as defined in claim 1, wherein said liquid composition is selected from the group of polyvinyl alcohols, polyacrylamides, and alcohol soluble nylons.

9. The invention as defined in claim 1, wherein said composition is polyvinyl alcohol.

10. The invention as defined in claim 9, wherein said polyvinyl alcohol has insolubilizer means added thereto.

11. The invention as defined in claim 8, wherein said polyvinyl alcohol is a high molecular weight, soluble in hot water.

12. The invention as defined in claim I, further characterized by applying an acrylic polymer coating over said film.

13. A method of reducing mercury vapor contamination of the ambient atmosphere from liquid mercury droplets disposed on an exposed surface, which method comprises, applying a metal powder to said surface, said metal being one that will amalgamate with mercury, and thereafter removing the amalgamated particles from the surface.

14. The invention as defined in claim 13 wherein the metal is selected from a group consisting of tin, bronze, copper and zinc.

15. The invention as defined in claim 13 further characterized by applying a catalyst to the surface after applying the metal powder.

16. The invention as defined in claim 13 further characterized by the step of scrubbing the surface with water and removing the water from said surface by vacuum means, and passing the vacuumed fluid through a water filter unit to entrap in the filter unit any amalgum contained in the fluid.

i i l= 

1. A METHOD OF REDUCING MERCURY VAPOR CONTAMINATION OF THE AMBIENT ATMOSPHERE FROM LIQUID MERCURY DROPLETS DISPOSED ON AN EXPOSED SURFACE, WHICH METHOD COMPRISES THE STEP OF APPLYING A METAL-POWDER TO THE SURFACE, THE METAL BEING ONE THAT WILL AMALGAMATE WITH MERCURY, THEREAFTER SCRUBBING THE SURFACE WITH WATER AND REMOVING THE WATER FROM THE SURFACE WITH VACUUM MEANS, AND PASSING THE VACUUMED FLUID THROUGH A WATER FILTER UNIT TO ENTRAP IN THE FILTER AND AMALGAMATED MERCURY CONTAINED IN THE FLUID, AND THEREAFTER COATING SAID SURFACE WITH A LIQUID COMPOSITION WHICH WILL SOLIDIFY TO A CONTINUOUS FILM WHICH IS SUBSTANTIALLY IMPERVIOUS TO MERCURY VAPOR.
 2. The invention as defined in claim 1, wherein the metal is selected from a group consisting of tin, bronze, copper, and zinc.
 3. The invention as defined in claim 1, further characterized by applying a catalyst to the surface after applying the metal powder.
 4. The invention as defined in claim 3, wherein said catalyst is a weak acid.
 5. The invention as defined in claim 4, wherein the acid is selected from a group consisting of acetic acid and phosphoric acid.
 6. The invention as defined in claim 1, further characterized by filtering the ambient atmosphere through a mercury vapor entrapping filter subsequent to applying said coating.
 7. The invention as defined in claim 6, wherein said filter is activated charcoal.
 8. The invention as defined in claim 1, wherein said liquid composition is selected from the group of polyvinyl alcohols, polyacrylamides, and alcohol soluble nylons.
 9. The invention as defined in claim 1, wherein said composition is polyvinyl alcohol.
 10. The invention as defined in claim 9, wherein said polyvinyl alcohol has insolubilizer means added thereto.
 11. The invention as defined in claim 8, wherein said polyvinyl alcohol is a high molecular weight, soluble in hot water.
 12. The invention as defined in claim 1, further characterized by applying an acrylic polymer coating over said film.
 13. A METHOD OF REDUCING MERCURY VAPOR CONTAMINATION OF THE AMBIENT ATMOSPHERE FROM LIQUID MERCURY DROPLETS DISPOSED ON AN EXPOSED SURFACE, WHICH METHOD COMPRISES, APPLYING A METHAL POWDER TO SAID SURFACE, SAID METAL BEING ONE THAT WILL AMALGAMATE WITH MERCURY, AND THEREAFTER REMOVING THE AMALGAMATED PARTICLES FROM THE SURFACE.
 14. The invention as defined in claim 13 wherein the metal is selected from a group consisting of tin, bronze, copper and zinc.
 15. The invention as defined in claim 13 further characterized by applying a catalyst to the surface after applying the metal powder.
 16. The invention as defined in claim 13 further characterized by the step of scrubbing the surface with water and removing the water from said surface by vacuum means, and passing the vacuumed fluid through a water filter unit to entrap in the filter unit any amalgum contained in the fluid. 